1. Field of the Invention
The present invention relates to a hand tool for cutting a hole in an object, and, more particularly, a hand tool for cutting a hole that has a larger diameter than the diameter of the cutting tool.
2. Description of the Related Art
U.S. Pat. No. 5,641,252 discloses a method for machining holes in a fiber reinforced composite material by using at least one cutting tool with wear resistant surface positioned eccentrically in relation to a central axis. The material is machined simultaneously in both an axial and a radial direction by causing the tool to move axially while rotating not only about its own axis, but also eccentrically about the central axis. In accordance with one particular characterizing feature of the invention, the workpiece is oriented in such a way that the axis of rotation of the tool is essentially orthogonal in relation to the longitudinal directions of the fibers in the immediate vicinity of the point where the tool meets the working surface. The diameter of the cutting tool is substantially smaller than the diameter of the hole that is produced. The eccentric rotary motion is generally a strictly rotary motion, i.e., it is executed with a constant distance between the central axis and the axis of rotation of the cutting tool. This distance between the central axis and the axis of rotation of the cutting tool can be increased by linear increments as the eccentric rotary motion continues.
This known method has a number of substantial advantages as compared with generally familiar techniques. For example, the method permits the production of holes without strength reducing damage. Also, the method permits the production of holes free from damage without having to preform a hole. Further, the method permits the production of holes to tight tolerances. The dimensional accuracy of the hole is determined substantially by the accuracy of the positioning of the tool relative to the central axis. The requirements imposed on the geometry of the cutting tool are not particularly high, on the other hand, since every individual tool is simply calibrated before use. Additionally, the method prevents the tool from becoming blocked. Since the diameter of the tool is substantially smaller than that of the hole, the method permits material removed by cutting to be carried away by simple means, such as with compressed air. The method also permits effective cooling of the tool and the edge of the hole. Yet another advantage is that the method substantially reduces the cost of wear compared to previously disclosed methods, due to the tool being coated with a wear resistant material, such as diamond coating. Moreover, this method also offers advantages when machining other materials such as metals.
U.S. patent application Ser. No. 09/092,467 discloses a spindle unit that includes a spindle motor that is rotatable about a principal axis. The spindle motor includes a tool holder having a tool axis substantially parallel to the principal axis. The tool holder is rotatable about the tool axis. An axial actuator is configured for moving the spindle motor in an axial feed direction substantially parallel to each of the principal axis and the tool axis. A radial actuator adjusts a radial distance between the principal axis and the tool axis. This spindle unit can be mounted in a stationary machine such as a CNC machine, robot or a simple rig.
PCT application PCT/SE94/00085 discloses a hand tool machine for machining holes according to the above described technique This disclosure relates to a hand machine for making holes in an object made of composite fibers, preferably with a curved surface. The center axis of the hole passes through a predetermined point on the surface of the object and is oriented in a certain direction relative to the longitudinal direction of the fibers of the object which are close to the point. The machine includes, in combination, a tool holder rotating about its own axis and a principal axis, a device for adjusting the axis of rotation of the tool holder in the normal direction of the surface at the point, a device for axial feeding of the tool holder relative to the object, a device for adjusting the radial distance between the principal axis and the axis of rotation of the tool holder, and a device for taking up the forces and moments between the machine and the object that result from the making of the holes.
Although this aforementioned disclosure outlines some principles, the disclosed hand tool does not offer a feasible and practical solution. One obvious limitation is that the disclosed concepts do not present a solution for the power supply and therefore their potential or realization must be questioned. One basic requirement for a hand tool is light-weight and user friendliness. The disclosed concepts do not provide a compact integrated light-weight design. Furthermore, the illustrated concepts show solutions which require a very long tool overhang, which is a severe limitation due to the radial cutting force, which creates a bending moment on the cutting tool.
When machining holes according to the proposed method, i.e., by positioning the tool eccentrically in relation to a cental axis and machining simultaneously in both an axial and radial direction by causing the tool to move axially and to rotate not only about its own axis, but also eccentrically about a central axis, the tip of the tool is subjected to both an axial force and a radial force. The radial force creates bending moment on the tool, the magnitude of which is dependent on both the magnitude of the force and on the length of the tool overhang (moment arm). It is desirable to minimize the bending moment for optimal machining accuracy. This can be achieved by minimizing the tool overhang, i.e., the free length of the tool. The concepts illustrated in PCT/SE94/00085 show situations where the tool overhang is determined by the thickness of the hole template and by the thickness of the workpiece. Since the thickness of the template may be substantial, the tool overhang may be accordingly substantial.